Euro 6 upgrades

[j789]

The buses with Euro 6 exhaust upgrades, once upgraded will the bus always be classed then as Euro 6 or  will the system need continued upgrading through its life due to normal degradation of the system for it to stay as Euro 6? 

[Tony]

The buses with Euro 6 exhaust upgrades, once upgraded will the bus always be classed then as Euro 6 or  will the system need continued upgrading through its life due to normal degradation of the system for it to stay as Euro 6?

They need the filters cleaning regularly to stay compliant, but if you don't do that it soon ruins the engine